Energy-based medical systems are often utilized to treat patients for various medical, cosmetic, and therapeutic reasons. For example, energy-based treatment systems may be utilized to heat selected areas and portions of a patient's tissue by applying energy to the tissue. Controlled heating of tissue often produces various beneficial effects, including improving the appearance of skin by removing or reducing wrinkles, tightening skin, removing unwanted hair, etc. Energy-based systems generate a signal, such as a radiofrequency (RF) signal, that is then applied to the patient. Generation of signals and delivery of these signals is often performed by a radiofrequency generator. To achieve optimum and desired energy delivery efficiencies, the output impedance of the radiofrequency generator's signal may be tailored to match the patient tissue load impedance. By definition, an impedance match is achieved when the overall net system reactance components are eliminated.
Energy-based medical systems include an energy transmission or signal path that begins at the radiofrequency signal generator, is directed to a patient through an electrode, propagates through the patient to a return electrode, and is returned through a return line to the signal generator. As with any transmission line, impedances along the energy transmission path must be matched to ensure efficient transmission of radiofrequency energy and to minimize reflected power arising from net impedance reactive components. If the impedances along the energy transmission path are not balanced, energy may be reflected within the energy transmission path, making the power and energy delivery inefficient. The reflected energy may inhibit the functionality of the system and consume excess energy. An impedance imbalance or mismatch may occur, for example, if the system component impedance fails to match (and counterbalance) the patient impedance.
Radiofrequency signal generators in conventional energy-based medical systems may include an additional impedance element adapted to match the system component impedance to the patient impedance. For example, signal generators may detect the system impedance and then select an additional conjugate impedance based upon the detected impedance so that overall system reactance is minimized. The impedance element may be, for example, a helical impedance tuning coil (e.g., inductor), or other similar device, positioned internally or proximate to the signal generator to balance a detected system capacitance.
Many energy-based medical systems utilize removable and replaceable electrode assemblies with working electrodes of different sizes and constructions and, hence, different impedances. The electrode assembly and electrode may be changed to adjust the treatment to different patients, to change the type of treatment, or to perform treatments of different types on the same patient. If so equipped, the signal generators in conventional medical systems must detect the change in impedance from the electrode swap and then select a new additional conjugate impedance. As mentioned above, the adjustment of the system impedance maintains an impedance balance that minimizes wasted energy. However, the dynamic range of the selectable additional impedance may be inadequate to handle a full range of working electrodes. In addition, the response time for adjusting the system impedance may be slow.
What is needed, therefore, are energy-based system electrode assemblies and handpieces that can efficiently and rapidly balance the overall system impedance.